Foundation method



Jilly 20, 1965 w. DEGEN 3,195,314

FOUNDATION METHOD Filed Feb. 26. 1962 Fig.7

United States Patent 3,195,314 FUUNDATHQN METHQD Wilhelm Began, Zeppelinallee 39, Frankfurt am Main, Germany Filed Feb. 26, 11.962, tier. No. 175,421 Claims. (@l. di -5h? The present invention relates to the foundation of prefabricated structural members or units by a special process.

In particular, it relates to the foundation of structural units prefabricated in a working area outside the area of excavation where such units are better accessible and may be produced with satisfactory density and stability, and may even be equipped with insulating boards and/ or protective layers before they are placed into the excavation, especially under water, where otherwise the construction work would be delayed by the need to work in a limited space and to keep this space dry.

The ordinary procedure in founding such prefabricated structural units is to level the base of the excavation, for instance, by skimmers operating under water, and to place the structural units onto the base thus leveled. Since, however, hollow spaces remaining between the foundation level and the load-carrying base of the structural member resulted in lumped loading calling for the assumption of the worst case in the static computation of the load, the ordinary procedure provides that the excavation be deeper than planned and that the space between the planned and the actual levels be filled with sand conveyed through pipelines to the space underneath the structural unit. As may be expected, this ordinary procedure is unsatisfactory inasmuch as the settlement of the loose sand under the structural unit can never be achieved at a uniform density throughout. For safety reasons, again very unfavorable lumped loading conditions have to be assumed in the static determination of the load distribution.

Contrariwise, it is an object of the present invention to provide a special process in which a dense packing is obtained in the soil used to lill the outer regions of the space between the planned level and the actual level, the remaining hollow spaces in the inner region being densely filled by injected settling substances as, for instance, cement mortar. I

It is another object of the invention to complete the backfilling around the structural unit in the excavation first, and to pack the soil from the backfilling under the structural unit thereafter.

Still another object of the present invention is to enhance the density of the soil at the actual excavation level by providing additional soil or by exchanging it against the soil encountered at the excavation level before lowering the structural unit into the excavation.

Finally, it is an object of the invention to inject the settling substance through the holes provided in the base of the structural member under pressure to obtain a high density of this substance.

The various features of the invention may become apparent in the description of the process to follow.

According to the invention, the structural unit prefabricated outside the excavation, that is, a member or plate, is lowered into the excavation and held in place by suspension or supports so that its base coincides with the planned level of the excavation one or two inches above the actually excavated level. Soil is now filled into the spaces between the sides of the structural unit and the walls of the excavation, and this soil may be, in part or in whole, the backfilling planned to surround the structural unit or member. This soil is then packed under the member preferably by the operation of depth jolters around the outer edges of the member. Where the base of the member is relatively large, the operation of depth jolters will pack the soil under the outer regions of the member base, thus leaving a hollow space underneath the central region of the member base. It is this hollow space hat is then filled by injection of a suitable substance, for instance, cement mortar, under pressure so as to ensure optimum density in the packing of this substance and to ensure a uniform distribution of this density. The soil previously packed around this central region and along the bottom edges of the member, forms a reliable damlike enclosure contributing in the building-up of the density desired.

To facilitate the injection process and the dense packing of the substance enclosed by the tamped soil, especially in the case of large-base members, holes or other apertures are provided in the base of the member. These holes serve not only the injection process, but also permits the insertion of measuring gauges; upon completion of the injection process, they can easily be sealed.

In cases where the soil of the actually excavated level has insufdcient capacity, the lowering of the member is preceded by densifying such soil by depth jolters or surface iolters operating under water and homogenizing the soil to a degree precluding the possibility of subsequent settlement under load.

Where the soil at the actuall excavated level cannot be densified and has an insufiicient load-carrying capacity, it may be exchanged against better grade soil that may be t en densified and homogenized in the manner described.

The novel features believed to be characteristic of the invention may best be understood by reference to the accompanving drav illustrating two stages in the application of the present invention by way of an example, in which FIG. 1 is the sectional view of an excavation or a trench filled with ground water and of a structural member suspended from a bridge crane; and

FIG. 2 is the sectional View of the same trench, backfilled, and with soil densely packed under the member edges as a result of depth joltin The structural member 1i in HG. 1 is suspended from a crane 2 into a trench 3 excavated, Without containing the water, to an actual depth somewhat exceeding the planned foundation level. When t.e member 1 is thus located in its planned position defined by the planned foundation level, there is a small space between the mem ber base and the actual level as indicated at 4 in FIG. 1. After partial or complete backiilling of the trench, the soil along and underneath the member edges is tamped and densiiied by a depth ioiter 5 in such a way that the edges of the member re now supported by this soil on which the load is uniformly distributed.

FlG. 2 is a sectional view of the same trench, backfilled, and with soil densely packed under and adjacent the lower edges of the structural member as a result of depth vibration. An aperture 6 is provided in the bottom of the structural member through which cement mortar is press-injected to fill the hollow space underneath the central region of the bottom of the structural member, after the soil along and underneath the lower edges of the member has been tamped and densilied. Small tubes '7 are inserted in the bottom of the structural member through which the injection process may be observed.

By preparing a foundation in accordance with the process of the present invention all the requirements as to the foundation are satisfied. In particular, it is ensured that the hollow space between the bottom of the structural member and the trench surface is completely and uniformly filled, thus eliminating the hazard of subsequent non-uniform settlement. The structural member is uniformly supported on the soil across its entire bottom surface. Hence, the static determination may proceed from the most favorable supporting conditions.

Another advantage of the present invention is that the construction work may be performed at a shorter time and at lower expenses, since not only no time is required for the construction and settling of the tructural member on the site but the trench may be excavated without the ordinary removal of water, as both the excavation and foundation work maybe performed under water.

In case of suhicient space on the site the excavation may be accomplished without reinforcing the trench. In such a case, the slopes of the trench may be made very steep, since they are then more resistant to the internal and external water pressure because of their being well balanced. The rigidity of the slopes of the trench may be considerably increased by artificially banking up the water in the trench. In all these cases no special safety measures are required with respect to the stability of the slopes, since the process according to the present invention dispenses with the necessity of workmen being present in the trench.

After the structural member has been moved to the desired position, which may be accomplished from the construction site, and upon baclrfilling of the space between the level of the trench and the lower side of the bottom of the structural member, and tamping of the soil, which may also be effected without it being neces-,

sary to enter the trench, the foundation work may be performed and observed through the small tubes 7 from the interior of the structural member.

Moreover, the rigidityof the slopes of the trench may be essentially increased by baclzfillin the trench as soon as the structural member has been placed into the desired position.

What is intended to be secured by Letters Patent is:

l. in a process of forming a foundation for prefabri cated structural units in soil, the steps comprising: firstly excavating a trench to a level substantially at least one and approximately two inches deeper than a planned foundation, secondly placing and supporting a structural member, having side walls and a bottom, in said trench above the bottom thereof at a depth corresponding to said planned foundation, thirdly filling soil around the side walls and the bottom of said structure and between said structural member and said trench and under the lower edges of said member, fourthly densifying said filled soil by packing to form a barrier to liquid under at least the lower edges of said member to the exclusion of open space between the edges of the member and the 3 trench bottom and finally filling the space extending under and towards the center of said member.

2. The process as claimed in claim 1 wherein the excavation is partially or completely tilled and tamped with backfill material, prior to densifying and tamping the soil underneath the bottom of said structural member by depth or internal vibrating means.

. 3. The process according to claim 1 in which a hardenable material is injected through an opening in the structural member into the space between the member and said trench and thereafter causing said material to harden.

4.111 a process of forming a foundation for pre-fabricated structural units having side Walls and a bottom, excavating a trench to an extent that the excavation is slightly deeper than the desired depth of the planned. foundation, lowering a structural member into said excavation and holding said member therein at a level where the lower-side of the bottom of said membercoincides with the level of said planned foundation, filling soil into the spaces between the side portions of said structural member and the walls of said excavation as well as underneath said structural member along and adjacent the lower edges thereof, densifying said soil around th side walls and the bottom of said structural member and filling the hollow space underneath the portions of said bottom of said structural member extending towards the center thereof by press-injecting a setting substance, such as cement mortar, in to said hollow space through apertures in the bottom of said structural member, until said hollow space is completely filled with said setting substance.

References Cited by the Examiner UNITED eras PATENTS 2,191,845 2/40 Bretting 61-63 2,667,749 2/54 Steverman 6136 FOREIGN PATENTS 425,092 1/ 11 France. 1,111,660 11/55 France, 95,510 9/60 Holland.

EARL 1., /VITMER, Primary Examiner.

JACOB SHAPIRG, JACOB L. NACKENOFF,

Examiners. 

1. IN A PROCESS OF FORMING A FOUNDATION FOR PREFABRICATED STRUCTURAL UNITS IN SOIL, THE STEPS COMPRISING: FIRSTLY EXCAVATING A TRENCH TO A LEVEL SUBSTANTIALLY AT LEAST ONE AND APPROXIMATELY TWO INCHES DEEPER THAN A PLANNED FOUNDATION, SECONDLY PLACING AND SUPPORTING A STRUCTURAL MEMBER, HAVING SIDE WALLS AND A BOTTOM, IN SUCH TRENCH ABOVE THE BOTTOM THEREOF AT A DEPTH CORRESPONDING TO SAID PLANNED FOUNDATION, THIRDLY FILLING SOIL AROUND THE SIDE WALLS AND THE BOTTOM OF SAID STRUCTURE AND BETWEEN SAID STRUCTURAL MEMBER AND SAID TRENCH AND UNDER THE LOWER EDGES OF SAID MEMBER, FOURTHLY DENSIFYING SAID FILLED SOIL BY PACKING TO FORM A BARRIER TO LIQUID UNDER AT LEAST THE LOWER EDGES OF SAID MEMBER TO THE EXCLUSION OF OPEN SPACE BETWEEN THE EDGES OF THE MEMBER AND THE TRENCH BOTTOM AND FINALLY FILLING THE SPACE EXTENDING UNDER AND TOWARDS THE CENTER OF SAID MEMBER. 